Detectable warnings, a distinctive surface pattern of domes detectable by cane or underfoot, are used to alert people with vision impairments of their approach to streets and hazardous drop-offs. The ADA Accessibility Guidelines (ADAAG) require these warnings on the surface of curb ramps, which remove a tactile cue otherwise provided by curb faces, and at other areas where pedestrian ways blend with vehicular ways. They are also required along the edges of boarding platforms in transit facilities and the perimeter of reflecting pools.
The technical specifications of the ADA require that detectable warnings on walking surfaces have a specific truncated dome pattern. This unique pattern is intended to provide a consistent and uniform surface that is distinctive from other materials and, therefore, recognizable as a warning to pedestrians that they are approaching a potentially dangerous area. Under the “Revised Draft Guidelines for Accessible Public Rights-of-Way,” the ADAAG specifically requires that detectable warnings consist of a surface of truncated domes aligned in a square or radial grid pattern.